Conventionally, in most cases where a high-resolution A/D converter is needed, a double-integration A/D converter using an operational amplifier (OP-AMP) is used.
There are some problems in implementation of a semiconductor chip for the double-integration A/D converter. For example, in case of a capacitor device as an integration device used in the double-integration A/D converter, large capacitance is required to integrate the capacitor device into the semiconductor chip.
In addition, the OP-AMP and other devices in the double-integration A/D converter are implemented with very complicated circuits. The double-integration A/D converter has a problem in that the circuits are complicated. In addition, the double-integration A/D converter has a problem in that additional physical circuits for amplifying an analog signal and removing noise are needed for measuring the analog signal which causes a very small change in a sensor.